Liquid electrostatographic developer compositions

ABSTRACT

An improved electrostatographic imaging process wherein the developer contains a toner release effective amount of a fatty acid ester. The addition of minor amounts of these esters to the developer or independent treatment of the imaging surface with said materials during cyclic operation of an electrostatographic imaging system facilitates developed image transfer and removal of toner residues from the photoconductive surface of the imaging member. This invention has application in electrostatographic imaging systems employing either liquid or dry modes of development. Apparatus used in this imaging system are also contemplated within the scope of this invention.

United States Patent [191 Mammino et al.

[ Dec. 24, 1974 LIQUID ELECTROSTATOGRAPHIC DEVELOPER COMPOSITIONS [73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Aug. 28, 1972 [21] Appl. No.: 284,319

Related US. Application Data [63] Continuation-impart of Ser. No. 873,105, Oct. 31,

1969, Pat, NO. 3,692,520.

[52] US. Cl. 252/62.1 [51] Int. Cl G03g 9/04 [58] Field of Search 252/62.l

[56] References Cited UNITED STATES PATENTS 3,079,270 2/1963 Cortez 252/621 OTHER PUBLICATIONS Moreno et al., Chemical Abstracts, Vol. 49, col. 638(e), 1955.

Primary Examiner-Ronald H. Smith Assistant Examiner-J. P. Branner [5 7] ABSTRACT An improved electrostatographic imaging process wherein the developer contains a toner release effective amount of a fatty acid ester. The addition of minor amounts of these esters to the developer or independent treatment of the imaging surface with said materials during cyclic operation of an electrostatographic imaging system facilitates developed image transfer and removal of toner residues from the photoconductive surface of the imaging member. This in vention has application in electrostatographic imaging systems employing either liquid or dry modes of development. Apparatus used in this imaging system are also contemplated within the scope of this invention.

1 Claim, 4 Drawing Figures LIQUID ELECTROSTATOGRAPHIC DEVELOPER COMPOSITIONS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 873,105, filed Oct. 3], 1969 now U.S. Pat. No. 3,692,520.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved electrostatographic imaging process, a developer composition, a method of treatment of an imaging member, the apparatus used in said treatment, the treated imaging member, and an apparatus provided with said treated imaging member. More specifically, the incorporation of specific fatty acid esters in electrostatographic developer compositions or independent application of said esters to the photoconductive surface of an imaging member used in such systems greatly facilitates developed image transfer and residual toner removal from such imaging surface. The use of these esters is compatible with an electrostatographic imaging system employing either a liquid or dry mode of development.

2. Description of the Prior Art The formation and development of images on the imaging surfaces of photoconductive materials by electrostatic means is well known. The basic process, more commonly known as xerography, involves forming a latent image on an imaging surface by placing a uniform electrostatic charge on the imaging surface of an imaging member and then exposing this electrostatically charged surface to a light-and-shadow image thereby selectively dissipating the charge in the irradiated areas. The resulting latent electrostatic image is then developed by depositing on said latent image a finely divided colored electroscopic material, known in the art as toner. This toner will be principally attracted to those areas on the imaging surface which retain the electrostatic charge, thereby rendering this latent image visible.

The developed image can then be read or permanently affixed to the imaging surface of the photoconductive substrate where this imaging surface is not to be reused. In the event that the imaging surface is of a reusable material and is to be used in preparation of subsequent xerographic copies, the developed image can be transferred to another substrate, such as paper, and then permanently affixed thereto. Various techniques have been devised to permanently affix this toner image to its substrate; including overcoating the toner image with a transparent film, and solvent or thermal fusion of the toner particles to the substrate material.

In electrostatographic processes employing drydevelopment systems, the electroscopic toner particles can be brought within the influence of the latent electrostatic image by anyone of a number of well known techniques. In general, the toner is either presented to the latent image by itself or in association with a carrier material. Examples of well-known dry development systems in which the toner alone is presented to the latent image are described in U.S. Pat. No. 2,221,776 (powder cloud development) and U.S. Pat. No. 2,895,847 (touchdown development). Carrier assisted development systems are also fully disclosed in the patent literature, including those systems described in U.S. Pat. No. 2,874,063 (magnetic brush development) and U.S. Pat. No. 2,6l8,552 (cascade development).

As indicated previously, development of the latent electrostatic images can also be achieved with liquid developing materials. Probably one of the better known liquid development systems, more commonly referred to as electrophoretic development, involves the dispersal of a finely divided charged pigmented material in an insulating carrier liquid; contacting the imaged areas of the imaging surface with this dispersion; and creating an electric field within this dispersion. The dispersed pigmented material will migrate under the influence of the field established within the dispersion and selectively deposit on the charged areas of the imaging surface in image configuration.

In yet another well-known liquid development system described in U.S. Pat. No. 3,084,043, both the pigment and a polar dispersing medium are attracted to the im aged areas on the imaging surface. This system offers distince advantages overthe previously described elec trophoretic development system since contact between the dispersal medium and the non-imaged areas of the imaging system is minimized thereby reducing the pos sibility of undersirable background and smearing of the image due to the presence of excess fluid on the imaging surface.

A third liquid development system described in U.S. Pat. No. 3,285,741 involves the uniformly contacting of a latent image bearing surface with liquid developer; however, due to the electrical properties of the developer only those charged areas on; the imaging surface are wetted by the developer.

Both the dry and liquid development systems of the type described above, wherein the latent electrostatic image is first developed on a reusable imaging member and then transferred to another substrate for fixation, suffer similar operational deficiencies; namely, the in' complete transfer of the developed image from the imaging member to the transfer sheet. Ths untransferred portion of the image and inadvertantly deposited toner particles remaining on the imaging member, hereinafter referred to as toner residues, must be removed from the imaging surface of the reusable imaging member in advance of the succeeding copying cycle in order to prevent ghost images" from appearing in subsequent copies and toner filming or build-up on the imaging surface. The problem of incomplete developed image transfer is most acute in a positive to positive reproduction sequence, since, in this type of imaging system, the toner is very strongly attracted and tightly held to the charged image areas on the photoconductive substrate, thereby making subsequent transfer of the entire toner image extremely difficult. Removal of these toner resi dues from the imaging surface can be somewhat facilitated by subjecting these persistently adhering toner particles to a neutralizing charge prior to attempting cleaning of the imaging surface.

The techniques and means used in removal of residual toner from a reusable imaging surface are varied and wellknown. Two of the more popular systems involve the use of specially adapted webs" or brushes and combinations thereof. A typical brush cleaning apparatus is disclosed by L. E. Walkup et al. in U.S. Pat. No. 2,832,977. Brush type cleaning means usually comprise one or more rotating brushes impinging upon the imaging surface, which during their operation brush residual powder from the plate into a stream of air which is exhausted through a filtering system. A typical web cleaning device is disclosed by W. P. Graff, Jr., et

al. in U.S. Pat. No. 3,186,838. According to the Graff 5 disclosure, removal of the residual powder from the plate is affected by the relative movement of a fibrous web material over the plate surface.

The sensitivity of the imaging member to abrasion, however, requires that special precautions be exercised during the cleaning phase of the copying cycle. For example, pressure contact between cleaning webs and imaging surfaces must be kept to a minimum to prevent rapid destruction of the imaging surface. One such means of protection of the photoreceptive surface is overcoating said surface with a protective film. Although protective coatings would protect the imaging surfaces for longer periods of time, the electrical properties of the imaging member layer impose certain limitations as to the acceptable maximum thickness of such a coating. Thick protective coatings are unacceptable since the method of their application to the imaging surface entails considerable inconvenience, expense and down-time. Application of such a coating will ordinarily involve removing the photoreceptor from the machine, preparing the eroded photoreceptor surface for reception of a new coating, applying the new coating, allowing the new coating to dry and reinstalling the newly coated photoreceptor into the copier. Certain extremely thin films, applied to the imaging surface as a pretreatment or in situ during the machine sequence, have proven successful (US. Pat. No. 3,501,294 to R. J. Joseph); however, the art is constantly on the lookout for improved films or at least practical alternatives. Furthermore, for reasons which are not entirely clear, toner particles are frequently difficult to remove from some photoreceptor coating materials, and toner accumulation on these coating materials causes deterioration of subsequent images formed on the photoreceptor surface in reusable imaging systems. Thus, there is a continuing need for a better system for protecting imaging surfaces, developing electrostatic latent images and removing residual developed images.

It is, therefore, the objective of this invention to provide an improved electrostatographic imaging process and developer composition to overcome the above noted deficiencies in the prior art.

Another of the objectives of this invention is to provide an improved electrostatographic imaging process enabling more complete developed image transfer and residual toner removal.

A principal objective of this invention is to provide an improved electrostatographic developer composition containing a filing additive which facilitates developed image transfer and residual toner removal.

Still yet further of the objectives of this invention include the provision of the apparatus for carrying out said improved imaging process and means for dispensing said derivative onto the imaging surface of the imaging member independent of the developer composition.

SUMMARY OF THE INVENTION The foregoing and related objectives of this invention are accomplished by providing an electrostatographic developer composition comprising an intimate mixture of finely divided toner particles and a toner release effective amount of at least one non-liquid ester of the formula R--(1[-1t;i-(t 1 wherein, R is hydrogen or CH (CH with 1 being an integer from 0 to 7;

with x being an integer from 0 to 8, and y being an integer from 0 to 7; and

R and R and R being independently selected from hydrogen or R with R being an aliphatic hydrocarbon of from 12 to 22 carbon atoms. with the proviso that said ester have at least one of R R and R being Esters encompassed within the above structural formula which are especially useful in both the developer and in independent treatment of the imaging member for improvement in toner release properties of said member include the lower alkyl ester of a fatty acid, e.g. glyceryl tri-( l2-hydroxystearate); propylene glycol monohydroxystearate; and ethylene glycol monohydroxystearate.

This invention also embraces an improved imaging process employing the above developer composition, and the apparatus associated with both the carrying of this imaging process and the dispersing of said ester onto the imaging surface independent of the developer composition.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view in vertical cross-section of an automatic electrostatographic copier having a continuous imaging member and an impregnated web arrangement for dispensing toner release agent.

FIG. 2 is an elevational view in vertical cross-section of a bar-brush arrangement for dispensing toner release agent on the imaging surface of an imaging member.

FIG. 3 is an elevational view in vertical cross-section of a bar-web arrangement for dispensing toner release agent on the imaging surface of an imaging member.

FIG. 4 is an elevational view in vertical cross-section of solid bar arrangement for dispensing toner release agent on the imaging surface of an imaging member.

DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS Developer Composition Electrostatographic developers of this invention comprise an intimate mixture of finely divided toner particles and a toner release effective amount of an ester also referred to throughout the disclosure as condensation product of a fatty acid and an akylene diol or triol. These compositions can be prepared by any of the known techniques commonly employed in preparation of liquid and dry developers. By the phrase toner release effective amount it is intended to describe functionally that concentration of ester that must be present in the developer or dispensed directly onto the imaging surface in order to accomplish the stated objectives of this invention. It will be appreciated by those skilled in the art that the precise amount of ester needed to facilitate image transfer and removal of toner residues from the imaging surface will vary depending upon the particular mode of development, the affinity of the toner for the imaging surface, the particular means employed for transferral of the developed image and removal of toner residues from the imaging surface, as well as other intangible factors. Good results can be obtained when from about 0.1 to about 1 weight percent of ester based upon the weight of the developer, is added to said developer composition.

Toner material which is employed in the present invention can be any electroscopic toner material that is perferably pigmented or dyed. Typical toner materials which are especially useful in dry developer systems include the following resin materials: polystyrene polyacrylic, polyethylene, polyvinyl chloride, polyacrylamide, methacrylate, polyethylene terephthalate. polyamide, and copolymers, blends and mixtures thereof. In addition, the following are also contemplated: gum co pal, gum sandarac, rosin, rosin-modified phenol formaldehyde resins, epoxy resins, and vinyl resins. These vinyl resins may be a homopolymer or a copolymer of two or more vinyl monomers. Typical monomeric units which may be employed to form vinyl polymers include: styrene, vinyl naphthaline, mono-olefins, such as ethylene, propylene, butylene, isobutylene; vinyl esters, such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; esters of alphamethylene aliphatic moncarboxylic acids such as methyl acrylate, ethyl acrylate, n-butyl acylate, isobutyl acrylate, dodecyl acrylate, noctyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; vinyl ethers such as vinyl methyl either, vinyl isobutyl ether, vinyl ethyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone; polyester toner materials of the type disclosed in U.S. Pat. No. 3,590,000; and mixtures thereof. Thermoplastic materials having a melting point or range starting at least about 1 F. are especially suitable for use in the developer composition of this invention.

Suitable materials employed as the toner will usually have an average molecular weight between about 2,000 to about 500,000 and sometimes even higher.

In liquid developer systems the toner can be a material similar to that employed in dry development systems or merely the pigment divorced from such thermoplastic material.

Any suitable pigment or dye may be employed in conjunction with the toner as a colorant if needed or desired. Examples of such colorants include carbon black, nigrosine dye, aniline blue, Calco oil blue, chrome yellow, ultramarine blue, duPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal and mixtures thereof. The pigment or dyes should be present in the toner in a sufficiently quantity to render it highly colored so that it will form a clearly visible image on a recording member. Thus, for example,

where conventional xerographic copies of typed documents are desired, the toner may comprise a black pigment, such as carbon black. Preferable, the pigment is employed in an amount of from about 1 percent to about 30 percent, by weight, based on the total weight of the colored toner. If the toner colorant is a dye, substantially smaller quantities may be used.

It is desirable that such toner materials be of a suffi ciently fine, powder like consistency to have the free flow characteristics and discrete dimensions necessary for development of latent electrostatic images of high resolution. Good results are obtained when such toner compositions have an average particle size, by weight percent, of less than about 30 microns.

In cascade and magnetic brush development systems, the development of the latent image is carrier assisted. Carrier materials which can be used to help convey the electroscopic toner particles from the developer reservoir to the imaging surface are well known in the xerographic art. These materials can comprise any suitable solid material capable of acquiring and retaining a charge opposite in polarity to the charged electroscopic toner particles so that when the two are physically combined, said toner particles are attached and cling to the surface of the carrier. When a positive re porduction of the electrostatic images is desired, the carrier particles are selected so that the toner particles acquire a charge having a polarity opposite to that of the electrostatic image. Alternatively, if a reversal reproduction of the electrostatic image is desired, the carrier is selected so that the toner particles acquire a charge having the same polarity as that of the electrostatic image. Thus, the materials for the carrier particles are selected in accordance with its triboelectric properties with respect to the electroscopic toner so that when mixed or brought into mutual contact, one component of the developer is charged positively if the other component is below the first component in a tri boelectric series and negatively if the other component is above the first component in a triboelectric series. By

proper selection of materials in accordance with their triboelectric effects, the polarities of their charge, when mixed, are such that the electroscopic toner particles adhere to and are coated on the surface of carrier particles and also adhere to that portion of the electrostatic image bearing surface having a greater attraction for the toner than the carrier particles. Typical carriers include: steel, flintshot, aluminum potassium chloride, Rochelle salt, nickel, potassium chlorate, granular zircon, granular silica, ferrites, methyl methacrylate, glass and the like. The carriers may be employed with or without a coating. Many of the foregoing and other typical carriers are described in U.S. Pat. No. 2,618,552. An ultimate coated particle diameter between about 50 microns to about 200 microns is preferred because the carrier particles then possess sufficient density and inertia to avoid adherence to the electrostatic images during the cascade development process. Adherence of carrier beads to electrostatic drums is undesirable because of the formation of deep scratches on the surface during the image transfer and drum cleaning steps. Also, print deletion occurs when large carrier beads ad here to xerographic imaging surfaces. For magnetic brush development, carrier particles having an average particle size less than about 800 microns are satisfactory. Generally speaking, satisfactory results are obtained when about 1 part toner is used with about 10 to about 1000 parts by weight of carrier in the cascade and magnetic brush developers.

The dispersal media commonly used in liquid development system, also traditionally referred to in the art as carriers, can be one or a mixture of liquid vehicles, including polar and nonpolar fluids, and aqueous and non-aqueous fluids.

It has been found particularly useful in the liquid developer system for the finely developed toner particles to be present in an amount of from about 15 to about 35 percent based on the weight of the developer composition.

Typical materials that may be employed as principal vehicles include glycerol, water, 2,5-hexanediol, polypropylene glycol, mineral spirits, 2 ethyl-1,3- hexanediol, mineral oil, benzyl alcohol, dipropylene glycol, paraffin oil, oleic acid, dihexyl phthalate, vegetable oils such as castor oil, rapeseed oil, sesame oil, cottonseed oil, corn oil, sunflower seed oil, olive oil, and peanut oil. Also included are fluorocarbon oils such as duPonts Freon solvents and Krytox oils, silicone oils, kerosene, carbon tetrachloride, toluene. In general, liquid developers resulting from the dispersion of the various toners and additives in the principal vehicle should have a conductivity in the range of from about 10 to about l0 (ohm-centimeters) to be useful in liquid development systems. However, since a thin film of developer ordinarily accumulates on the surface of a recycling photoconductor, adequate charge retention of the photoconductor for each cycle is difficult to maintain. For these reasons, it is preferred to employ a vehicle having a conductivity less than about 10 (ohm-cm). Any hydrocarbon oil having this conductivity may be used. Typical vehicles within this group include mineral oil and the vegetable oils, including castor oil, peanut oil, sunflower seed oil, corn oil, rapeseed oil, and sesame oil. Also included are oleic acid, kerosene, silicone oils and fluorocarbon oils.

In addition to the above principal vehicles, an auxiliary or secondary vehicle may be employed to impart or adjust any one or more of the properties of the principal vehicle. For example, minor amounts of a secondary vehicle can be added to the principal vehicle to improve dispersion of the toner; to adjust viscosity of the developer; or to enhance the principal vehicles wetting capability.

Moreover, the secondary vehicles should preferably exhibit properties in common with the principal vehicle such as being nonodorous, non-hygroscopic, and of low volatility to provide a stable developer with a nonoffensive odor. An additional function of secondary vehicles may be to help the developer penetrate into the photoconductor or copy paper. Typical materials that may be employed as either primary or secondary vehicles include dibutyl phthalate, butyl isodecyl phthalate, butyl octylphthalate, diisooctyl phthalate, di-2-ethyl hexyl phthalate, isooctyl isodecyl phthalate, normal octyl decyl phthalate, diisodecyl phthalate, ditridecyl phthalate, isodecyl tridecyl phthalate, diisooctyl adipate, di-2- ethyl hexyl adipate, isooctyl isodecyl adipate, normal octyl decyl adipate, diisodecyl adipate, diisooctyl sebacate, di-2-ethyl hexyl sebacate, polyadipate ester, polyadipate ester, isooctyl palmitate, butyl stearate, butyl oleate, triethylene glycol dicaprylate, triethylene glycol caprylatecaprate, triethylene glycol dipelargonate, diethylene glycol dipelargonate, butanediol dicaprylate, triisooctyl trimellitate, tri l-ethyl hexyl trimellitate, mixed normal trialkyl trimellitate.

A more comprehensive description of the essential and optional ingredients of the liquid developer compositions of this invention can be found in U.S. Pat. No. 3,692,520 which is hereby incorporated by reference.

The ester(s) employed in the developer composition of this invention is the product of the condensation of a fatty acid and an alkylene diol or triol. These fatty acids are preferably substantially saturated although some degree of unsaturation can be tolerated. The degree of condensation of fatty acid on these polyhydric compounds need not be complete, and, thus the ester can also have free hydroxyl groups. Preparation of these esters can be achieved by standard laboratory technique using readily available reagents and equipment.

Fatty acids which are used in preparation ofthese esters can be described as monobasic, aliphatic hydrocarbons having a hydrocarbon chain length in the range of from about 12 to 22 carbon atoms. The hydrocarbon chain can be saturated or unsaturated and can have a limited number of pendant functional groups along its backbone, e.g. hydroxyl. Representatives of the fatty acids which can be used in preparation of the ester component of the developer include stearic acid, oleic acid, palmitic acid, linoleic acid, linolenic acid and ricinoleic acid.

Polyhydric materials which readily react with the above fatty acids to from the corresponding ester are typically alkylene diols and triols having from 2 to 10 carbon atoms. Included within this group of polyhydric materials are ethlene glycol, glycerol, 1,3-butylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, l,2,4- butanetriol, l,5-pentanediol, 1,6-hexanediol, 1,2,6- hexanetriol, 1,7-heptanediol, 1,8-octanediol, l,9- nonanediol, l,l0decanediol.

As indicated previously, the ester can be prepared from the above materials by standard processing techniques. Representatives of esters which fall within the scope of products of the condensation of the above fatty acid and polyhydric compounds are ethylene glycol monostearate, ethylene glycol mono-(hydroxy stearate), ethylene glycol distearate, ethylene glycol monolaurate, ethylene glycol dilaurate, ethylene glycol monooleate, ethylene glycol dioleate, ethylene glycol monoricinoleate, ethylene glycol diricinoleate, ethylene glycol monopalmitate, ethylene glycol dipalmitate, propylene glycol mono-(hydroxy stearate), propylene glycol monostearate, propylene glycol distearate, glyceryl tri-(12-hydroxy stearate), glyceryl tristearate, glyceryl monostearate, glyceryl 1,3-distearate, glyceryl triricinoleate, glyceryl monooleate, glyceryl monoricinoleate, glyceryl monopalmitate, glyceryl 1,3- dipalmitate, glyceryl tripalmitate, glyceryl mondaurate, glyceryl monolinoleate, glyceryl dilinoleate, glyceryl trilinolenate, glyceryl monolinoleate, glyceryl dilinoleate, glyceryl trilinoleate, 1,4-butylene glycol monoleate, l,4-butylene glycol dipalmitate, 1,4-butylene glycol distearate, 1,4-butylene glycol mono-(hydroxy stearate), 1,4-butylene glycol monoricinoleate, 2,3- butylene glycol dilaurate, 2,3-butylene glycol diricinoleate, 2,3-butylene glycol monopalmitate, l,2,4- butanetriol tristearate, l,2,4-butanetriol-l ,4'dilaurate, 2,3,4-butanetriol-2-monooleate, l,2,4-butanetriol-2,4- diricinoleate, l,5-pentanediol dilinoleate, l,5- pentanediol mono-(hydroxy stearate), l,5-pentanediol dipalmitate, 1,5-pentanediol dioleate, 1,6-hexanediol diricinoleate, l,6-hexanediol monolaurate, l,2,6- hexanetriol tristearate, 1,2,6-hexanetriol-l ,-dioleate, 1,8-octanediol diricinoleate, 1,8-octanediol monostearate, 1,8-octanediol monolaurate, 1,8-octanediol monolinoleate, 1,9-nonanediol distearate, I,9- nonanediol monooleate, l,l-decanediol dilinoleate, and l, l O-decanediol monstearate.

It has been found particularly useful in the above dis cussed liquid developer for the esters to be present in amounts of from about 0.1 to about 1 percent based on the weight of the liquid developer composition.

During the cyclic operation of a typical electrostatographic copier, the imaging surface of the reusable imaging member is periodically or continuously treated with a predetermined amount of one or more of the esters of the type disclosed herein. When the ester is included as an integral component of either a dry or liquid developer, the imaging surface is subjected to treatment with ester during the development phase of each copying cycle. In this mode of treatment, an adherent film of ester is deposited over substantially all of the imaging surface after only a few copying cycles. This film can be described as either a continuous or discontinuous coating. Improvement in image transfer and residual toner removal is often evident even after subjecting the imaging surface to only one pass with developer. Control over the amount of ester deposited on the imaging surface is critical since excessive deposition of this toner release agent can adversely affect both imaging and development in an electrostatographic imaging system. Ordinarily, in liquid development systems an average ester film thickness of about 3 microns or less will provide a good balance between the imaging, development and toner release properties of the photoconductive surface. In dry development systems this film should not exceed about 250A. A number of the esters specifically enumerated above are liquid under ambient conditions and, therefore, for reasons which should be apparent to one skilled in the art would be less preferred than solid material as an additive to a dry developer composition. Both the liquid and non-liquid esters of the developers of this invention could, however, be applied to the imaging surface of the imaging member independent of the developer by a variety of well-known techniques. For example, the liquid esters could be applied in predetermined amounts to the imaging surface by a wick-like arrangement or in the form of an aerosol. Similarly, those esters which are solid under conditions ordinarily prevailing during routine operating conditions can be transferred to the photoconductive surface by any of a number of well-known techniques.

The process of application of the non-liquid esters to the imaging surface of an imaging member independent of the developer is hereinafter described by reference to FIGS. 14. Referring initially to FIG. 1, an automatic electrostatographic copier is shown which comprises a drum-like imaging member 17, having a light sensitive insulative layer 16 operatively associated with an electrically conductive substrate 9 rotatably mounted to enable the light sensitive insulative layer or imaging surface of the imagingmember to sequentially pass in the direction indicated by the arrow past a plurality of electrostatographic processing stations located peripherally to the imaging surface.

For the purposes of the present disclosure, the several electrostatographic processing stations located peripherally to the imaging surface are functionally typical of those routinely employed in an electrostatographic reproduction cycle and can be described as fol lows.

A charging station 8, preferably located as indicated in FIG. 1 comprising a corona discharge device which includes an array of one or more corona discharge electrodes 7 partially enveloped within a shield 6 and energized from a high potential source 5, ionizes the air proximate to the imaging surfaceof the imaging member, thereby imparting a uniform surface charge thereto. Once charged, that portion of the imaging surface bearing the surface charge is subjected to expo sure by a light image at exposure station 4 wherein an optical scanning projection system projects an image onto the charged imaging surface from a stationary original therby forming a latent electrostatic image on said imaging surface.

The imaging surface bearing this latent electrostatic image then revolves to a development station 10 where a developer 11 is drawn from a sump 12 to a rotatable applicator sleeve 13 by a pick-up magnet 14 located within the applicator sleeve. As the applicator sleeve rotates in the direction indicated by the arrow, the attracted developer frictionally moves with the applicator sleeve to a brush forming magnet 15 (also located within the applicator sleeve), resulting in alignment of the developer along the lines of flux generated by the brush forming magnet between the applicator sleeve and the imaging surface 16 of the imaging member 17. The aligned developer particles form a soft brush-like structure 18 which, upon counterrotation of the applicator sleeve and the imaging member wipes the imaging surface, selectively depositing developer particles on the imaged areas of the imaging surface.

After the applicator sleeve bearing the brush-like de veloper structure revolves beyond development zone 19, the developer passes under the influence of a third magnet 20 located within a pick-off sleeve 33. As the pick-off sleeve revolves in the direction indicated by the arrow, developer particles, attracted by the internal field of magnet 20 are transferred from the applicator to the pick-off sleeve and consequently transported to a replenishment zone 21. In this replenishment zone additional toner and carrier are added to the recovered developer and the resultant mixture tumbled through a series of angularly inclined baffles 22 returning ultimately to the sump. This baffle arrangement should provide for uniform distribution of developer in the sump in order to insure presentation of a continuous supply of developer along the surface of the applicator sleeve disposed opposite pick-up magnet .14. Positioned subsequent to the developer station along the arc of travel of the imaging member is an image transfer station 32, where a transfer sheet 23, such as paper, is fed in coordination with the presentation of the developed image on the drum. Concurrent with presentation of the transfer sheet opposite the developed image, an electrostatic field is created by a corona discharge device 24 on the underside of the transfer sheet so as to effectively tack the develped image to the transfer sheet. This synchronous movement of the transfer sheet along the imaging member permits transfer of the developed image to this sheet where it can be subsequently more permanently affixed by means of heat fusion device or other well known techniques. After the developed image is transferred to the receiving sheet and the receiving sheet picked off the drum, substantially all residual toner particles remaining on the imaging surface are removed by impinging a doctor blade 26 in a chiseling attitude against said imaging surface. Upon removal of substantially all residual toner particles from the imaging surface, said imaging surface is contacted with a fibrous web material 27 which has been impregnated with one or more of the aforedescribed esters. As this impregnated web advances over the imaging surface in the direction indicated by the arrow an adherent film of ester is deposited over substantially all of said imaging surface.

In FIG. 2, the imaging surface is treated with ester by a rotating brush 29 impinging upon the imaging surface of the imaging member. As the brush rotates, it picks up the ester from an erodible bar 28 which is fed at a controlled rate toward the brush.

In FIG. 3, the imaging surface is treated with ester in the manner illustrated by FIG. 1; however, the ester is applied to the fibrous web 30 topically by controlled feeding of an erodible bar 28 against the surface of the web prior to the web impinging upon the imaging surface of the imaging member.

In FIG. 4, the ester is dispensed directly onto the imaging member by controlled feeding of an erodible bar 28 against the imaging surface. In each of the above specific embodiments illustrated in FIGS. 1-4, the depth of the ester film on the imaging surface is controlled by the same doctor blade used in removal of toner residues.

As will be appreciated by those skilled in the xerographic art, the apparatus described above can be readily modified to substitute a liquid development station of the type desclosed in for example, FIG. 4 and accompanying text of U.S. Pat. No. 3,084,043, for the magnetic brush developing station shown in FIG. 1.

The same functional limitation with respect to the quantity of ester which can be applied to imaging surface via a developer composition, apply in those instances where the ester is applied to an imaging surface independent of the developer. Good results can be obtained where the ester is applied to the photoconductive surface in quantities ranging from about 300 to 500 milligrams per square meter of photoconductive surface. The heretofore defined limitations with respect to average film thickness also apply in those instances where ester is dispensed on the photoconductive surface independent of developer.

Since the average film thickness is of critical importance, it must be maintained within the previously set forth operational limits. The depth of the ester film on the photoconductive surface can be determined spectophotometrically by monitoring reflectance from the photoconductive surface at a treated and an untreated area on this surface. Other more elaborate techniques using radioactive materials are also available to the art for determining film thickness, but do not readily lend themself to incorporation into an automatic imaging system. In the event that the quantity of ester is either below or in excess of predetermined levels, the ester film thickness can be adjusted either by dispensing additional material or by activation or increase in efficiency of a cleaning station within the copier for removal of excessive amounts of ester. For example, the ester film thickness on the photoconductive surface of the imaging member of this invention can be maintained at desired levels by a doctor blade set at a chiseling attitude against the imaging surface.

Imaging Member The imaging member referred to hereinabove in discussion of the developer, process and apparatus of this invention can comprise any known reusable electrostatographic imaging surface. The physical shape and dimensions of this element can vary with the type and function of apparatus in which it is employed. For example, in an automatic or cyclic copying system, the imaging member will usually be either drum shaped, having a reusable imaging surface on its exterior wall, or an endless or a disposable belt. Other apparatus may call for the imaging member to be in the form of a plate; and under such circumstances the imaging layer will usually be on at least one of the surfaces of the plate. This imaging member can be provided with either a conventional photoconductive or nonphotoconductive surface. Well'known photoconductive materials include vitreous selenium; zinc oxide; organic or inorganic photoconductors embedded in a nonphotocon ductive matrix; inorganic or organic photoconductors embedded in a photoconductive matrix; and homogeneous organic photoconductors, typified by polyvinyl carbazol charge transfer complexed with 2, 4, 7-trinitro fluorenone photoconductive material. Representative patents which disclose contemplated photoconductive materials include U.S. Pat. Nos. 2,803,542; 2,970,906;

3,131,006; 3,121,007; 3,151,982 and 3,484,237. The preferred imaging member used in the process and apparatus of this invention has a selenium based imaging surface on a rigid electrically conductive substrate, such as aluminum. The physical shape of this reusable imaging member should preferably be suited for cyclic or automatic operation in an electrostatographic copying system.

The application and maintenance of an adherent film of ester on at least a portion of the imaging surface of this type of electrostatographic imaging member protects the imaging surface from abrasion, facilitates image development, developed image transfer and minimization of toner filming or buildup on the imaging surface. The exact mechanism by which the previously described ester(s) achieve such suprising and advantageous results is not as yet known.

PREFERRED EMBODIMENTS The Examples which follow further describe, define and illustrate specific embodiments of the composition, process, and apparatus of this invention. Examples I, XV, XVII, XIX, XXIII and XXIX are included to provide a standard against which the performance of the treated imaging members can be gauged. Process conditions and apparatus specifications, where not explicitly set forth, are presumed to be standard and as hereinbefore described.

EXAMPLE I The vitreous selenium photoconductive drum of an automatic electrostatographic copier is corona charged to a positive voltage of about 800 volts, exposed to a light and shadow image thereby forming a latent electrostatic image on the imaging surface of the drum, and developed by the hereinbefore described magnetic brush technique using a standard polystyrene-carbon black toner blend; the average particle size of toner particles being about I2 microns. After development, the developed image is transferred to a sheet of paper, the paper bearing the developed image picked off the drum, the toner image fused on the paper, and the residual toner particles then removed from the imaging surface by a doctor blade set against the imaging surface at a chiseling attitude.

Initial copies reveal good copy quality in all respects; however, after 500 copies image quality is markedly inferior showing high background density, poor image fill and decreased image resolution. Inspection of the drum reveals a highly visible toner film buildup on the imaging surface.

EXAMPLE II The toner laden drum of Example I is removed from the copier, thoroughly cleaned and reinstalled in the copier. The apparatus is then modified by the addition of a toner release agent dispensing station between the doctor blade and the charging station. This dispensing station comprises a fibrous web material impregnated with the ester, glyceryl tri-( l2-hydroxystearate). As the vitreous drum rotates through its copy reproduction cycle, an adherent film of this ester is deposited over substantially all the imaging surface of this imaging member in the manner shown in FIG. 1. Copy quality remains relatively constant even after 500 copies in comparison to Example I, and inspection of the imaging surface of the drum does not reveal undesirable toner buildup of the type experienced in Example I.

EXAMPLES III XIII Example II is repeated except for substitution of the following esters for glyceril tri-(12-hydroxystearate).

Example No. Ester Ill ethylene glycol monostearate IV ethylene glycol mono-(hydroxystearate) V propylene glycol monostearate VI propylene glycol monothydroxystearate) VII ethylene glycol di( IZ-hydrostearate) VIII 1,6 hexanediol diricinoleate IX 1,8 octanediol monolaurate X 1,5-pentanediol dioleate/LS- octanediol monolinoleate (:0.3 parts by weight) XI l.2,4-butanetriol-2-oleate/ LlO-decanediol dilinoleate (0520.3 parts by weight) XII glyceryl tristearate XIII 1,3-glyceryl distearate In each of Examples II-XIII, copy quality after 500 copies was better than Example I and preceptibly less toner residue appeared on the imaging surface of the photoconductive drum than observed in Example I.

EXAMPLE XIV atively constant even after 500 copies in comparison to Example I, and inspection of the drum does not reveal undesirable toner buildup of the type experienced in Example I.

EXAMPLE XV Example I is repeated except that the copier is equiped with a poly-N-vinylcarbazole photoconductive imaging member of a type disclosed in US. Pat. No. 3,484,237. Here, as in Example I, toner filming of the photoconductive surface of the imaging member is observed after only 500 copies with noticeable deterioration in copy quality.

EXAMPLE XVI Example XV is repeated except that (a) the toner laden photoconductive imaging member of Example XV is replaced by a clean, unused imaging member of the same composition, and (b) copier is modified by the addition of a toner release agent dispensing station between the doctor blade and the charging station. This dispensing station comprises a fibrous web material im pregnated with the ester, glyceryl tri-(IZ- hydroxystearate). As the flexible photoconductive imaging member rotates through its copy reproduction cycle, an adherent film of ester is deposited over sub stantially all of its imaging surface in the manner illustrated in FIG. 1. Copy quality remains relatively constant even after 500 copies in comparison to Example XV, and inspection of the flexible photoconductive member does not reveal the undesirable toner filming of the type observed in Example XV.

The procedure used in evaluation of the liquid developer compositions of this invention is as follows.

A commercial Type E selenium xerographic plate having a surface layer of selenium about microns thick available from Xerox Corporation, Rochester, N.Y. is charged and exposed to a light and shadow image in the conventional manner. The electrostatic latent image thus formed is developed by moving a patterned surface applicator roll having developing quantities of developer in the depressed portions thereof past the image bearing surface so that liquid developer is pulled out of the depressed portions to the image bearing surface in image configuration. The speed of developer applicator is about 10 inches per second. The developer on the photoconductor in image configuration is then transferred to copy paper by standard procedures, and the selenium plate wiped clean with a cotton cloth to remove developer residues. However, all the developer is not removed and after the first cycle a thin film is observed to remain on the plate.

EXAMPLE XVII The imaging process outlined above is followed employing a liquid developer of the following composition:

Drakeol 9 Microlith CT Black Rucoflex TG-8 Ganex V216 Nigrosine S51] 38 parts by weight 38 parts by weight 9 parts by weight l4 parts by weight 0.24 parts by weight carbon black pigment manufactured by CIBA composed of about 40 percent carbon black pigment and 60 percent ester gum resin. Rucoflex TG-8 is a triethylene glycol dicaprylate manufactured by Hooker Chemical Company which serves as a solvent for the resinated carbon black pigment and may be regarded as a secondary vehicle in this formulation. Ganex V216 is an alkylated polyvinyl pyrrolidine compound manufactured by GAF Corporation which serves as a pigment dispersant and may also be regarded as a secondary vehicle. Nigorsinne SSJJ is a spirit soluble nigrosine dye manufactured by American Cyanamid Company.

The resolution of the first print is about 10 line pairs per millimeter. The procedure outlined above is re peated using the same selenium plate. After each cycle the film of residual developer left on the selenium plate is observed to increase in thickness and the print observed on the third cycle has lost all fine detail, the resolution having dropped to only about 2 line pairs per millimeter.

EXAMPLE XVIII The imaging process outlined above is repeated using a developer of the composition of Example XVII which has been modified by the addition of 0.7 parts by weight glyceryl tri-( l2-hydroxystearate).

The print obtained from the first duplicating cycle has a resolution of about 10 line pairs per millimeter. After repeated cycling the film of residual developer is observed to build up to a level of about 3 microns and thereafter remains substantially unchanged. Resolution is observed to diminish to about 6 to 7 line pairs per millimeter after about 25 cycles and to remain stable at this level for an additional 100 prints.

EXAMPLE XIX A zinc oxide paper backed binder layer photoconductor is charged and exposed in conventional manner. The developer described in Example XVII, except for the omission of nigrosine, is applied in doctored configuration to a rotatably mounted cylindrical roll having a patterned surface such that developer is present in the valleys or depressed portions of the applicator while the raised portions are substantially free of developer. The applicator roll thus loaded with developer is rolled across the zinc oxide paper bearing an electrostatic latent image whereby the attractive forces of the image pull developer from the applicator onto the zinc oxide paper in image configuration. The developer on the zinc oxide paper is transferred to receiver paper in image configuration in the conventional manner. The print obtained on the receiver paper had a resolution of line pairs per millimeter and an image density of 0.8.

EXAMPLE XX The procedure of Example XIX is repeated employing the developer composition described in Example XVIII, absent the nigrosine dye component. The print obtained on the receiver sheet has a resolution of 8 line pairs per millimeter and image density of 0.8. In comparison with the print of Example XIX, the prints thus obtained are sharper with less feathering of developer into the receiver sheet being observed.

EXAMPLE XXI The procedures followed in Examples XVII and XIX are repeated with the exception that the developer is of the following compositions:

Pale 34 parts by weight Rucoflex TG-8 33 parts by weight Ganex V216 8 parts by weight Microlith CT Black 24 parts by weight Thixcin R 0.6 parts by weight Pale 170 is an oxidized castor oil and Thixcin R is hydrogenated castor oil which is principally glyceryl tri-( l2-hydroxystearate) both available from Baker Castor Oil Company. Results substantially the same as those in Examples XVIII and XX respectively are observed.

EXAMPLE XXII The procedures followed in Examples XVII and XIX are repeated with the exception that the developer is of the following compositions:

Oleic Acid 66 parts by weight VM 550 33 parts by weight Propylene Glycol Monohydroxystearate) 0.5 parts by weight VM 550 is a methyl violet tannate pigment flushed in mineral oil to about a 50 percent by weight dispersion available from Magruder Color Company. Results substantially the same as those in Examples XVIII and XX respectively are observed.

EXAMPLE XXIII The procedures followed in Examples XVII and XIX are repeated with the exception that the developer is of the following compositions:

Sunflower Seed Oil Rucoflex TG-8 Ganex V216 Microlith CT Black Ethylene glycol mono- (hydroxystearate) 38 parts by weight 9 parts by weight 14 parts by weight 38 parts by weight 0.8 parts by weight Results substantially the same as those in Examples XVIII and XX respectively are observed.

EXAMPLE XXIV The procedures followed in Examples XVII and XIX are repeated with the exception that the developer is of the following compositions:

Flexicin-P6 62 parts by weight Ganex V216 30 parts by weight Statex B12 8 parts by weight Ethylene glycol di (l2-hydroxystearatcl EXAMPLE XXV The procedure followed in Example XVII is repeated except that 0.3 parts by weight of 1,6 hexanediol diricinoleate is added to the developer composition. The print obtained from the first cycle has a resolution of about 9 line pairs per millimeter. With repeated cycling a film of developer is observed to build up on the xerographic plate to about 3 microns and thereafter remains substantially unchanged. The resolution of the 4th through the 25th print is observed to be about 6 line pairs per millimeter.

EXAMPLE XXVI The procedure followed in Example XVII is repeated except that 0.4 parts by weight of 1,8 octanediol monolaurate is added to the liquid developer composition. Results substantially the same as those in Example XXV are observed.

EXAMPLE XXVII The procedure followed in Example XVII is repeated with the exception that the developer is of the following compositions:

Sunflower Seed Oil 38 parts by weight Rucoflex TG-8 9 parts by weight Ganex V216 14 parts by weight Microlith CT Black 38 parts by weight l,8-Octanediol Monolinoleate 0.3 parts by weight 1,5-Pentanediol Dioleate 0.5 parts by weight EXAMPLE XXVIII The procedure followed in Example XXVII is repeated except that 0.8 parts by weight of mixture of equal parts by weight of 1,2,4 butanetrioc 2 monooleate and 1,10 decanediol dilinoleate is substituted for the mixture of 1,8 octanediol monolinoleate; 1,5 pentanediol dioleate. Results substantially the same as those in Example XVII are observed.

EXAMPLE XXIX The vitreous selenium photoconductor drum of an automatic copying machine is corona charged to a positive voltage of about 800 volts and exposed to a light and shadow image to form an electrostatic latent image. The drum is then rotated through a magnetic brush development station. The control developer used in this process comprises 2 parts toner, which contains a commercially available styrenen-bytuI methacrylate copolymer, colored with carbon black, and about 100 parts of commercially available steel shot carrier beads. These toner particles have an average particle size of about 12 microns and the carrier beads an average particle size of about 125 microns.

After the latent image is developed, the resulting toner image is transferred to a sheet of paper at a transfer station and toner residues removed by means of synthetic rubber doctor blade held at a chiseling attitude to the photoreceptor.

Initial copies reveal good copy quality in all respects, however, after about 500 copies, image quality is markedly inferior showing high background density, poor image fill and decreased resolution. Inspection of the drum reveals substantial toner filming on its imaging surface.

EXAMPLE XXX The procedure followed in Example XXIX is repeated except the developer is modified by the addition of the ester, glyceryl tri-(l2-hydroxystearate) having an average particle size distribution of from 0.5 to 10 microns. The modification is effected by mechanically uniformly mixing 0.25 percent, by weight, of the ester based on the weight of toner, with the toner. Thereafter, the toner and ester are mixed with the carrier.

After 500 cycles, copy quality remains good in comparison with Example I and no deleterious toner film buildup was seen on the photoreceptor.

EXAMPLE XXXI XLI Example XXX is repeated except for the substitution of the following esters for glyceril tri-( l2- hydroxysterate Example No. Ester XXXI ethylene glycol moniostearate XXXII ethylene glycol mono-(hydroxystearate) XXXIII propylene glycol monostearate XXXIV propylene glycol mono-(hydroxystcarate) XXXV ethylene glycol di(l2-hydroxystearatc) XXXVI 1.6 hexanediol diricinoleate XXXVII 1.8 octanediol monolaurate XXXVIII 1.5-pentanediol dioleate/l ,8-

octanediol monolinoleate (5:3 mixture) XXXIX l,2.4-butanetriol-2mleate/ 1.10-decanediol dilinoleate (5:3 mixture) XL glyceryl tristcarate XLI Lil-glyceryl distearate weight of the developer composition. 

1. AN ELECTROSTATOGRAPHIC DEVELOPER COMPOSITION COMPRISING A LIQUID DISPERSION HAVING A CONDUCTIVITY IN THE RANGE OF FROM ABOUT 10**4 TO ABOUT 10**15 (OHM-CENTIMETERS)-1 COMPRISING A CARRIER LIQUID HAVING DISPERSED THEREIN FROM ABOUT 15 TO ABOUT 35 PERCENT OF FINELY DIVIDED TONER MATERIAL BASED ON THE WEIGHT OF THE DEVELOPER COMPOSITION AND FROM ABOUT 0.1 TO ABOUT 1 PERCENT OF GLYCERYL TRI-(12-HYDROXY STEARATE) BASED ON THE WEIGHT OF THE DEVELOPER COMPOSITION. 